The Coen brothers' critique of violence seems hypocritical, given all the carnage

Directors tread a tightrope whenever they set out to criticise violence. Cinematic brutality, unlike the real thing, can be such an electrifying spectacle that it takes a saint to resist administering those volts of unsavoury pleasure to the audience. Clint Eastwood spent most of Unforgiven showing how harrowing it is to kill another human being, before ruining all that conscientious work in a big, nonchalant shoot-out. And it would have been easier to swallow David Cronenberg's History of Violence as a critique of man's inhumanity to man if the fight sequences were not so utterly bitchin', to use the technical parlance.

Now Joel and Ethan Coen fall spectacularly into the same trap with their adaptation of Cormac McCarthy's novel No Country for Old Men. The Coen brothers haven't resembled world-class film-makers since their nutty masterpiece The Big Lebowski ten years ago, so it's good to see them regaining confidence here. Their customary iciness doesn't thaw out in the heat of the Tex-Mex locations: some heart-stopping sequences make the first half of this thriller no fun for old tickers. And the Coens are still dab hands at pointed visual gags, as demonstrated in the clothing store where rows of spotless Stetsons are mounted on the wall, like the scalps of a hundred Texans.

Beneath this controlled surface, the picture transmits some highly contradictory signals, addressing the futility of violence and yet exploiting the kick we get from seeing sadistic acts performed with relish.

The atrocities are carried out by the soft-spoken bogeyman Anton Chigurh, played by Javier Bardem in a floppy bowl cut that's less a hairdo than a hair-don't. It takes some perversity to hire one of cinema's sultriest heart-throbs and make him look like Bernard Bresslaw, but the Coens are nothing if not contrary.

Chigurh carries with him a mysterious canister of compressed gas, which he uses for those tricky household chores - blasting off locks, killing people, that sort of thing. One man calls him a ghost. Another claims he's crazy, which goes without saying. In fact, he turns out to be the personification of mortality and violence, which must be a huge disappointment for his mother.

He is certainly a man of his word, which is bad news for Llewelyn Moss (Josh Brolin), as Chigurh has vowed to kill him and his wife, Carla Jean (the excellent Kelly Macdonald, bringing a little fresh air to this macho hothouse). Moss has made the colossal error of strolling off with a case of loot that he found amid the bloody debris of a desert massacre. The bounty belongs to Chigurh. Now he wants it back, and he's not going to ask nicely. Hoping to prevent the Moss family from joining the list of fatalities is Sheriff Bell (Tommy Lee Jones), a wise old coot struggling to comprehend Chigurh's actions and the notion of evil itself. While he's at it, he could try working out what the film is saying.

The Coens could have stayed on-message by moving all the violence off-screen, making us register instead the dread of its approach and the horror of its aftermath. Frustratingly, there are even moments when that appears to be their plan, and you glimpse the kind of picture this might have been. The most frightening scene, in which Chigurh intimidates an elderly gas-station attendant, doesn't depict so much as a hangnail or a stubbed toe, but its menace is overwhelming. And some of the murders are kept discreetly out of view, the camera arriving on the scene after the body grows cold - or not at all.

But the picture has no compunction about using carnage for cheap thrills so long as the victims in question are deemed disposable: the anonymous Mexicans, for instance, who meet the business end of Chigurh's shotgun in assorted motel rooms.

Something important is lost in any film when we are encouraged to overlook or endorse an act of aggression - that's exploitation. In a picture which professes concern about violence, and even features one character, Sheriff Bell, who thinks about little else, it's called hypocrisy. That makes No Country for Old Men an exasperating and self-defeating experience, rather like listening to a nymphomaniac extol the virtues of celibacy.

Ryan Gilbey is the New Statesman's film critic. He is also the author of It Don't Worry Me (Faber), about 1970s US cinema, and a study of Groundhog Day in the "Modern Classics" series (BFI Publishing). He was named reviewer of the year in the 2007 Press Gazette awards.